In a coal liquefaction process, valuable liquid products of lighter molecular weights are obtained from heavy hydrocarbonaceous materials such as coal, tar sands and the like, using a transition metal catalyst, e.g., molybdenum disulfide. As the process progresses, most of the molybdenum typically becomes concentrated in the metals bearing materials, solid residue or heavy bottoms.
Various approaches have been introduced to recover the transition metal components from the spent coal liquefaction catalysts. U.S. Pat. No. 6,153,155 discloses a process in which the solid residue is coked then followed by combustion at a range of 800° C. to 1900° C. The flue dust is treated with ammonia and ammonia carbonate to obtain ammonium molybdate. U.S. Pat. No. 4,417,972 discloses a process in which the insoluble molybdenum sulphide is converted to soluble molybdenum oxides for subsequent recovery of molybdenum as molybdate. U.S. Pat. No. 4,417,972 discloses a process in which the solid residue is reacted with sulphuric acid in the presence of methanol and an oxidizing agent such as hydrogen peroxide to extract molybdenum into the aqueous phase.
There is still a need for an improved and simple process to recover transition metals including but not limited to molybdenum from coal liquefaction residues.